1. Technical Field
The invention relates to devices for forming the image of a remote object, suitable for operation throughout a wide range of the spectrum.
There exist more and more applications for which the same optical device must supply the image of a remote object to sensors operating in different wavelength ranges, for example to a television camera operating in the visible spectrum (0.4.mu. to 0.7.mu.), to a silicon tube television camera operating from 0.4 to 1.mu., to a sensor operating in the near infrared, to a receiver associated with a CO.sub.2 laser at 10.6.mu.. None of the materials transparent for the whole of the range from 0.4 to 14.mu. is truly appropriate for forming multispectral objective lens common to several sensors, for most of these materials are hygroscopic and those which are not so, have an excessive chromatic dispersion.
2. Prior Art
Devices are further known comprising mirrors for forming the image of a remote object and in particular different types of telescopes. But the known optical mirror devices, although they have the advantage of good efficiency over a very wide frequency range and complete absence of chromatism, on the other hand have two drawbacks which up to now have prohibited their use for numerous applications: most existing systems have a high central obturation and a small field, generally not exceeding 4.degree..
There is also known (French 1,393,577) a collimator having a primary paraboloid mirror and a secondary hyperboloid mirror which are mutually aligned and have common focuses. The arrangement has all hereinbefore-mentioned drawbacks. The provision of an additional elliptical mirror does not remove them.